Fabrication and characterization of WO(3)/Ag/WO(3) multilayer transparent anode with solution-processed WO(3) for polymer light-emitting diodes

The dielectric/metal/dielectric multilayer is suitable for a transparent electrode because of its high-optical and high-electrical properties; however, it is fabricated by an expensive and inefficient multistep vacuum process. We present a WO(3)/Ag/WO(3) (WAW) multilayer transparent anode with solution-processed WO(3) for polymer light-emitting diodes (PLEDs). This WAW multilayer not only has high transmittance and low resistance but also can be easily and rapidly fabricated. We devised a novel method to deposit a thin WO(3) layer by a solution process in an air environment. A tungstic acid solution was prepared from an aqueous solution of Na(2)WO(4) and then converted to WO(3) nanoparticles (NPs) by a thermal treatment. Thin WO(3) NP layers form WAW multilayer with a thermal-evaporated Ag layer, and they improve the transmittance of the WAW multilayer because of its high transmittance and refractive index. Moreover, the surface of the WO(3) layer is homogeneous and flat with low roughness because of the WO(3) NP generation from the tungstic acid solution without aggregation. We performed optical simulation and experiments, and the optimized WAW multilayer had a high transmittance of 85% with a sheet resistance of 4 Ω/sq. Finally, PLEDs based on the WAW multilayer anode achieved a maximum luminance of 35,550 cd/m(2) at 8 V, and this result implies that the solution-processed WAW multilayer is appropriate for use as a transparent anode in PLEDs.